1. Field of the Invention
The present invention relates to a lens driving device which moves a zoom lens group or a focus lens group forward and backward in a photographic optical axis direction, and more particularly, to a lens driving device which transmits a driving force via a lead screw.
2. Description of the Related Art
Conventionally, a lens driving device includes a lens driving device which transmits the rotational force of a stepping motor to a lead screw via a gear.
The lens driving device which transmits the rotational force of a stepping motor to a lead screw via a gear will be described with reference to FIG. 11.
FIG. 11 is a cross-sectional view of essential parts of a first conventional lens driving device.
As shown in FIG. 11, a lead screw 107 has a fitting portion 107b formed at a base 107c of a male screw 107a positioned at one end side of the lead screw 107, and the fitting portion 107b is rotatably supported by only one position of a support hole 101a formed in a CCD base plate 101.
A holding portion 107d having a spherical surface (sphere R) shape is provided at a position spaced apart from the base 107c of the lead screw 107. The holding portion 107d abuts on a gear cover 108. The lead screw 107 is thereby held on the CCD base plate 101.
That is, the lead screw 107 is supported at only one end on the CCD base plate 101 with the top end portion of the lead screw 107 on the male screw 107a side not being supported. A gear 106 is fixed between the fitting portion 107b and the holding portion 107d of the lead screw 107, to thereby transmit the rotational force of a stepping motor to the lead screw 107.
FIG. 12 is a cross-sectional view of essential parts of a second conventional lens driving device (see Japanese Laid-Open Patent Publication (Kokai) No. 2007-219147). The same components as those in the lens driving device of FIG. 11 are designated by the same reference numerals.
In FIG. 12, a conical support portion 207d is provided at a position spaced apart from the base 107c of the lead screw 107. The conical support portion 207d is fittingly supported in a support hole 208a formed in a gear cover 208 in a rotatable manner. The lead screw 107 is supported between the CCD base plate 101 and the gear cover 208.
At this time, the lead screw 107 and the gear cover 208 are in a line contact state in which the conical support portion 207d of the lead screw 107 and a hole end portion (edge) of the support hole 208a of the gear cover 208 abut on each other. Through the abutment, the lead screw 107 is held between the CCD base plate 101 and the gear cover 208.
Because of the above configuration, the lead screw 107 can be supported in a stable state. The top end of the lead screw 107 is prevented from swinging. Also, a change in operating load due to the tilting of the lead screw 107 is reduced.
In the first conventional lens driving device (FIG. 11), the fitting portion 107b of the lead screw 107 is supported by only one position of the support hole 101a of the CCD base plate 101. Thus, when the lead screw 107 is rotated, the top end of the male screw 107a of the lead screw 107 swings due to a fitting play generated between the fitting portion 107b and the support hole 101a, thus a lens stop position cannot be stabilized.
In the second conventional lens driving device (FIG. 12), the problem in the former one is improved. That is, by providing the lead screw 107 with the conical support portion 207d and fittingly supporting the conical support portion 207d in the support hole 208a formed in the gear cover 208 in a rotatable manner, a centering function is provided, thereby stabilizing the lens stop position.
In the second conventional lens driving device, the conical support portion 207d of the lead screw 107 is supported in the line contact state with the support hole 208a of the gear cover 208. Thus, there is such a problem that driving load is increased relative to the first conventional lens driving device having the spherical surface (sphere R) shape holding portion 107d abuts on the gear cover 108 and is in point contact therewith.